What is a light year supposed to measure ‍♂️?

A)Time
or
B) Distance
:)

Different isotopes indicate that an element will have different numbers of

Which function is performed by earths atmosphere? a. ultraviolet rays are prevented from reaching the ozone layer. b. earths temperature is raised and moderated by trapping in heat c. charged particles from the sun are prevented from reaching earth. d. magnetic charges from space are prevented from reaching earths surface.

From the choices provided below, list the reagent(s) in order that will react with cyclopentanone to form the compound shown below.